Practical organic and bio-chemistry / by R.H.A. Plimmer.

  • Robert Plimmer
Date:
1915
Catalogue details

Licence: Public Domain Mark

Credit: Practical organic and bio-chemistry / by R.H.A. Plimmer. Source: Wellcome Collection.

    22/660 (page 2)
    RECOGNITION OF AN ORGANIC COMPOUND. Organic compounds are distinguished from inorganic compounds by being combustible: on heating they generally char, sometimes take fire, and on prolonged heating completely burn away leaving no ash. Inorganic compounds when heated do not char and they leave a residue. A mixture of an organic compound and an inorganic compound will also char and leave a residue. There are a few excep- — tions to this general rule: oxalic acid and its salts amongst the organic compounds do not char on heating; amongst the inorganic com- pounds the ammonium salts volatilise leaving no ash. An oxalate leaves a residue of the oxide of the metal with which it is combined, The following experiments exemplify these statements :— 1. A small piece of paraffin wax heated upon platinum foil will melt, take fire, and will completely burn away leaving no residue. 2. Accrystal of cane sugar heated in the same way will melt, char, and on further heating will disappear completely. 3. A few crystals of common salt heated on platinum foil will melt, and unless heated very strongly, e.g. with a blowpipe flame, will remain as a solid white mass when allowed to cool. 4. A small piece of soap heated as above will char, the vapours evolved _-may take fire, and when the charred particles have all vanished a white or nearly white residue will remain. NVote.—TIt ts in this way that substances composed of organic and inorganic matter are recognised. The composition of the inorganic residue is found out by the usual methods of inorganic analysis after the organic matter has been destroyed by heating. 5. No appreciable change will be seen on heating a little oxalic acid or an oxalate, e.g. calcium oxalate. | 6. Ammonium chloride volatilises on heating and leaves no residue. 7. To prove the presence of carbon in oxalic acid or in an oxalate the sub- stance is heated in a small glass tube and the gases evolved are passed into lime or baryta water. A precipitate of calcium or barium carbonate indicates the presence of carbon. | 8. On heating ammonium chloride as in 7, there is no formation of carbonate.